I mainly look at my largest winning or losing hands, and I use a program called PokerSnowie to get a somewhat objective opinion about, if I played the hand correctly. I dont follow the advice of the program 100% though, because in some situations I deliberate take exploitative lines, that I think are good, against bad players.
If you dont have a program like that, you simply look at the hand with the luxury of not being on the clock and with
real money at stakes, and ask yourself, if you would still have played it the same way. And if unsure, ask the opinion of others in the hand review session of for instance this forum.
As for more trivial decisions in smaller pots like preflop ranges, or when to C-bet, this is really something, you should try to learn once and for all, so you have it ingrained. It makes no sense to review exact hands to figure out, if it was a good idea to open A8o from UTG at 6-max or to C-bet it out of position on KJ4 rainbow against two opponents.